I was going to say, are you just blindly replacing drive shafts on a "oops there goes another drive shaft" basis? Surely it's a rubbing issue and that should be sorted before another one is fitted. ANY decent mechanic, or anybody who knows anything about cars could point out where it's rubbing. Have a look, it's not easy to see without getting under the car/turning the wheels/getting wet and covered in grit, but its worth a look.
Any noise? Vibrations?